Mild chemistry synthesis of ultrathin Bi 2 O 2 S nanosheets exhibiting 2D-ferroelectricity at room temperature.

Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi 2 O 2 S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi 2 O 2 S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi 2 O 2 S nanosheets arises due to the local distortion of Bi 2 O 2 layers, which destroys the local inversion symmetry of Bi 2 O 2 S.